<template>
    <el-scrollbar ref="scrollContainer" :vertical="false" class="scroll-container"
                  @wheel.native.prevent="myHandleScroll">
        <slot/>
    </el-scrollbar>
</template>
<script lang="ts">
    import {Component, Provide, Ref, Vue} from "vue-property-decorator";

    @Component({
        components: {}
    })
    export default class ScrollPane extends Vue {
        @Provide() private tagAndTagSpacing: number = 4;// tagAndTagSpacing
        @Provide() private left: number = 0;
        @Ref("scrollContainer") private scrollContainer: any;

        scrollWrapper(): any {
            return this.scrollContainer.$refs.wrap;
        }

        myHandleScroll(e: any) {
            const eventDelta = e.wheelDelta || -e.deltaY * 40;
            this.scrollWrapper().scrollLeft += eventDelta / 4;
        }


        moveToTarget(currentTag: any) {
            const $container = (this as any).$refs.scrollContainer.$el;
            const $containerWidth = $container.offsetWidth;
            const $scrollWrapper: any = this.scrollWrapper();
            const tagList = (this as any).$parent.$refs.tag;

            let firstTag = null;
            let lastTag = null;

            // find first tag and last tag
            if (tagList.length > 0) {
                firstTag = tagList[0];
                lastTag = tagList[tagList.length - 1];
            }

            if (firstTag === currentTag) {
                $scrollWrapper.scrollLeft = 0;
            } else if (lastTag === currentTag) {
                $scrollWrapper.scrollLeft = $scrollWrapper.scrollWidth - $containerWidth;
            } else {
                // find preTag and nextTag
                const currentIndex = tagList.findIndex((item: any) => item === currentTag);
                const prevTag = tagList[currentIndex - 1];
                const nextTag = tagList[currentIndex + 1];

                // the tag's offsetLeft after of nextTag
                const afterNextTagOffsetLeft = nextTag.$el.offsetLeft + nextTag.$el.offsetWidth + this.tagAndTagSpacing;

                // the tag's offsetLeft before of prevTag
                const beforePrevTagOffsetLeft = prevTag.$el.offsetLeft - this.tagAndTagSpacing;

                if (afterNextTagOffsetLeft > $scrollWrapper.scrollLeft + $containerWidth) {
                    $scrollWrapper.scrollLeft = afterNextTagOffsetLeft - $containerWidth;
                } else if (beforePrevTagOffsetLeft < $scrollWrapper.scrollLeft) {
                    $scrollWrapper.scrollLeft = beforePrevTagOffsetLeft;
                }
            }
        }

        mounted() {
            this.scrollWrapper();
        }
    }
</script>

<style scoped lang="scss">
    .scroll-container {
        white-space: nowrap;
        position: relative;
        overflow: hidden;
        width: 100%;

        > > > .el-scrollbar__bar {
            bottom: 0;
        }

        > > > .el-scrollbar__wrap {
            height: 49px;
        }

    }
</style>

